1. Field of the Invention
This invention relates to a control apparatus for a voltage controlled-type switching device such as an insulated gate bipolar transistor (IGBT), to control conduction and shutoff of the switching device.
2. Description of the Related Art
As one type of control apparatus, for example the apparatus disclosed in Japanese Patent Application Laid-open No. 2008-141841 is known.
This apparatus of the prior art comprises a driving circuit which causes conduction and shutoff of the switching device, and a current sensor which detects the current flowing in the switching device.
Further, the apparatus of the prior art comprises a first comparison circuit which compares the current detected by a current sensor with a first reference value, and when the detected current is equal to or greater than the first reference value, outputs an overcurrent detection signal indicating an overcurrent in the switching device.
Further, the apparatus of the prior art comprises a second comparison circuit which compares the current detected by the current sensor with a second reference value, and when this detected current is equal to or greater than the second reference value, outputs a pass-through current detection signal indicating a current passing through the switching device.
Further, the apparatus of the prior art shuts off the switching device when the time duration of an overcurrent detection signal output from the first comparison circuit is equal to or greater than a first regulation time, or when the time duration of a pass-through current detection signal output from the second comparison circuit is equal to or greater than a second regulation time.
In an apparatus of the prior art comprising such a configuration, when there is an overcurrent or a pass-through current in the switching device, by shutting off the switching device, surge voltage occurring at the time of current shutoff of the switching device can be suppressed.
However, such an apparatus of the prior art has the problem that, when the switching device is not in an overcurrent state, but suppression of surge voltages at the time of current shutoff of the switching device is necessary for the purpose of protection from overcurrents, such surge voltage suppression is not possible.